Previously, self-contained gas springs have been constructed with an actuating rod connected to a piston slidably received in a cylinder having a chamber which is precharged at a predetermined pressure, such as 2,000 psi, with an inert gas such as nitrogen. When the rod and piston are forced into the chamber, the gas therein is compressed to a maximum operating pressure which is usually in the range of about 3,000 to 5,000 psi, depending on the volume of the chamber and the effective area and stroke of the piston. In normal use, the pressure to which a self-contained gas spring is initially charged is not varied or changed. The spring is initially charged, relieved and recharged through a high pressure poppet core valve of the type commonly used for aircraft struts and accumulators.
Previously, a plurality of gas springs each having a chamber port connected to an external gas source also have been used. Each chamber port was connected to a common manifold by a flexible hose so that all of the chambers could be charged with gas to the same pressure from a common source of gas at a high pressure such as a tank. This manifold permits the pressure to which the spring chambers are charged to be varied, controlled and, as needed for different applications, changed from time to time. However, when the gas springs are used, the interconnecting hoses are subjected to pressure surges, fluctuations and heating which eventually produces leaks and ruptures. Thus, these manifold systems require considerable maintenance and repair and shielding of the hoses and pipes to avoid potential safety hazards, if they rupture. Moreover, in use, several gas springs can produce such large pressure surges and generate so much heat in the working gas that it is usually necessary to utilize surge tanks in the system to decrease the extent of the pressure surges and dissipate sufficient heat so that the maximum pressure of the working gas does not exceed a safe maximum level and result in rupturing or damaging of the springs, hoses or pipes of the system. In some of these systems check valves have also been used to decrease gas surges.